Carrier-current system



May 12, 1925 v 3,537,099

' H. J. VENNES Y CARRIER CURRENT SYSTEM Filed Dec. 21, 1920 PatentedMay'l2, 1925 UNITED STATES PATENT OFFICE.

HARALD J. VENNES, OF NEW YORK, N. Y., ASSIGNOR WESTERN ELECTRIC COM-PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

CARRIER-CURRENT SYSTEM.

Application filed December 21, 1920. Serial No. 432,816.

To all whom. it may concern:

Be it known that I, HARALD J. VENNES, a citizen of the United States,residing at New York, in the county of Bronx, State of New York, haveinvented certain new and useful Improvements in Carrier-Current Systems,of which the following is a full, clear, concise, and exact description.

This invention relates to carrier current systems and more particularlyto means for improving the quality of the signal supplied to atransmitting circuit.

It is a well-known fact that the frequency supplied by a vacuum tubeoscillator, such as is used in carrier current systems, is to aconsiderable degree dependent on the impedance of the load circuitconnected to the oscillator.

It is also a fact that when an alternating voltage, impressed on theinput circuit of a vacuum tube device, has an amplitude suflicient tomake the grid positive with re s ect to the filament, a grid currentwill ow 'andhence lower the input impedance of the device. Hence, whenin a carrier telea h system the output of an oscillator o e s into theinput of an amplifier, it is obvious that the impedance-of t esecircuits when connected to other will depend upon the amplitude of theoscillations to be impressed on the am lifier. This amplitude may bedetermined y using apotentiometer to interconnect theamplifier andoscillator but when the potentidmeter setting is changed the outputimpedance will be changed and as a result the frequency of theoscillations will be caused to vary.

Again, in such systems whonsignals are being transmitted, the sendingrelay connects a low impedance path across the output circuit of theoscillator with the result that a sur e will occur at the beginning andY end of eac signal. This seems to be caused by a suddenchange offrequency at these points in the signal periods: hence, sharp si a1efl'ects are impossible.

e primary object of'this invention is to provide means whereby sharpsignal effects may be obtained.

Another object of this invention is tov provide means which willstabilize the frequency of the oscillations produced by an oscillator.

A further object is to rovide an arrangelt" ment in which the impe anceof the circuit external to the oscillator circuits will be maintainedsubstantially constant.

These objects and others which 'will. appear as the nature of theinvention is disclosed, may be accomplished by inserting a largeresistance in the circuitexternal to the oscillator, so that theimpedance chan es in said circuit due to the adjustment of t epotentiometer or transmission of signals will not introduce materialchanges in the impedance of the output circuit of the oscillator. Inthis manner, the tendency of impedance changes in the external circuitto react upon the oscillator and change the frequency of theoscillations produced thereby is avoided.

Different circuit arrangements embodying the invention are shown in thetwo res of the attached drawings, wherein F1g.,1 shows an arrangement inwhich the oscillator is connected to theamplifierthrough .apotentiometer and Fig. 2 shows an arrangement in which the oscillatorconnected to the amplifier.

Referring to Fi 1 an oscillator of the type, described by V. L. Hartleyin his patent for oscillation generators, No. 1,356,763, issued October26, 1920, isillustrated. Thi's oscillator comprises a space dischargedevice 1 having its grid or control electrode and its anode connected tothe opposite terminals of an inductance 3, and its cathode connected toan intermediate point thereon. In shunt to this inductance 1s a variablecondenser' 4 which cooperates with inductance 3 to constitute a tunedcircuit adaipted to determine the frequency of the osci ationsgenerated. By varying the inductance 3, condenser 4, or both, the he isdirectly quency of the oscillations may be varied.

ductance to revent short-circuiting of the oscillations t roughthesources 5 and 6.

Condensers 7 and 8, designed to impose an infinite impedance to the flowof direct current but to permit alternating current to pass without apreciable attenuation, are in- :serted in the temating current paths ofthe oscillator circuits which connect the filament heating source 5 tothe midpoint of .the inductance 3 and the plate source 6 to tensity ofthe electromotive force supplied to the grid circuit of the amplifier 10may be regulated by adjusting the contact 11 associated with theresistance 9. Included in the circuit connecting the adjustable .contact11 and the grid of the amplifier 10 is a resistance 12, which will-bereferred to later, and associated with said circuit between theresistance 12 and the grid is a path 13 adapted to be grounded to eflectsi al transmission. A condenser is inserte in this path to prevent theflow of direct current from the grounded sources therethrough, whilepermitting the flow of oscillations when this circuitis completed.

A key has been herein shown to control the ground path. Any other means,for

example,' a line relay controlled by a distant or local operator, maybe'u'sed for this purpose.

When no signals are being transmitted, the oscillations impressed uponthe grid circuit of the amplifier will cause current variations of thesame frequenc in the plate current of the amplifier. This variablecurrent is supplied to the tuned circuit constituted by the adjustablecondenser 15 and the primary winding of the transformer 16,

the secondary of which may be connected either to a transmission line orthe antenna of a radio system, whereby oscillations of definitefrequency will be transmitted to the distant receiving station.

When it is desired to transmit a message to a remote station, the groundpath 13 is closed and opened in accordance with any desired code toshunt the oscillations from the amplifier input circuit, thussuppressing the flow of variable current in its output circuit and hencethe transmission of energy to the distant station.

Plate current is supplied to the output circuit of the amplifier 10 by asource 17 through a retard coil 18, which serves to prevent the flow ofthe oscillations through the source 17 while permitting the flow ofdirect current from the source through the plate circuit of theamplifier.

A blockin condenser 19 is inserted between the p ate source and thetuned circuit to prevent direct current supplied by the source 17 fromreaching tuned circuit 1516, though offering substantially no impedanceto the flow of alternating curing conditions stated above.

Referring to Fig. 2 the invention is shown applied to a system employingmetallic or ungrounded circuits. In this gure the oscillator is of thesame type as that shown in Fig. 1, but is directly connected to theamplifier 10 through the resistance 12. The signal path 13 is connectedacross the input circuit of the amplifier at a point between resistance12 and the grid, and the potentiometer 911 is placed in the alternatingcurrent output circuit of the amplifier to control the amplitude of thecurrent supplied to the transformer 16 and therethrough to the loadcircuit.

In the arrangement shown in both of these figures, the operation of thesystem is the same. Normally an alternating current .of frequencylargely determined by thenatural period of the tuned circuit 2 issupplied to the load circuit. Upon completion of the signal circuit 13,the supply of alternating-current is cut off so that silent and activeintervals follow one another in any desired order determined by theopen- .ing and closing of the signaling circuit;

hence, signals or spaces may be represented by either silent or im ulsereceiving intervals in accordance with the code decided upon.

In an arrangement. which did not include the resistance 12, .thecompletion of the signal path 13 caused a lowering of the impedance ofthe out t circuit of the oscilator, sincethe por ion, of the inductance3 in the input circuit of the tube'l was thereby shunted through aportion of the resistance 9, in Figure 1 or short-circuited in Figure 2.When this occurred, the tuning of the oscillatory circuit was subjectedto variations due to the above mentioned change in the impedance acrossa portion of the inductance 3 and surges occurred both upon the openingand closing of the signal path. Resistance 12, by eliminating surges,sharpened the signal periods.

Since the form of carrier current supply is immaterial from an operativeviewpoint it will be apparent that any other type of oscillator orsource of supply may be utilized. Again complete wire circuits may beused in the arrangement shown in Fig. 1 and. ground connections willbeequally effective in thedesign shown in Fig. 2. The circuit changesnecessary in either case being evident it is believed to be unnecessaryto describe them further.

While the particular form of devices utilized and circuit connections emloyed have been described inorder to clearly and completely set forththe invention, it is to -be understood, that this invention is notlimited to these specific features but only by the scope of the appendedclaims.

What is claimed is 1., A signal system comprising a source forcontinuously generating a current of.

carrier frequency, said source including a tuned frequency determiningcircuit, a work circuit connected thereto including an amlifier, meansto shunt the carrier current 2'0!!! said amplifier in accordance withsignals and means to maintain substantially constant impedanceconditions in said work circuit irrespective of the operation-of saidshunting means.

2. A signal system comprising a source for continuously generating acurrent of carrier frequenc said source including a tuned frequencyetermining circuit, a work circuit connected thereto includinganamplifier, means to divert the carrier current from said amplifier inaccordance with signals and means between said source and divertingmean's to maintain substantially constant impedance conditions" in saidwork circuit irrespective of the operation of said diverting means.

3. A signal system comprising a source for continuously generating acurrent of carrier frequency, said source including a tuned frequencydetermining circuit, an amplifier connected thereto, means to interruptthe flow of carrier current to said amplifier in accordance with signalsand means to prevent changes in impedances external to said source fromreacting upon said frequency determining circuit.

4. signal system comprising a vacuum tube oscillation generator, a loadcircuit connected'thereto including an amplifier, a controlled shuntpath for the oscillations supplied by said generator, and reactionsuppressing means included in said load circuit between said generatorand the path.

5. Asignal system comprising a vaccum tube oscillation generator, 9.load "circuit connected thereto including a resistance and an amplifier,a controlled shunt circuit con nected to said load circuit adjacent'tosaid amplifier, and means to control said shunt circuit.

6. A signal system comprising a vacuum tube oscillation generator, aload circuit connected thereto including a resistance and an amplifier,a controlled shunt circuit connected to said load. circuit between theresist-ance'and amplifier, and means to control said shunt circuit.

7. A signal system comprising a source of carrier current, a loadcircuit connected thereto including an impedance and an amplifier, aground circuit connected to said oad circuit between the impedance andamplifier, circuit.

8. A signal system comprising a source of carrier current, a circuitconnected to said source including reaction suppressing means and anamplifier, and means to ground the terminal of the reaction suppressingmeans which is adjacent to the amplifier.

9. A signal system comprising a vacuum tube oscillation generator, acircuit connectand 'means to control the ground ed thereto includingreaction suppressing.

means and an amplifier, and means to ground the terminal of the reactionsuppressing means which is adjacent to the amplifier.

' 10. A signal system comprising a vacuum tube oscillation generator, acircuit connected thereto including a resistance and an amplifier, andmeans to ground the terminal of the resistance which is adjacent to theamplifier.

11. The combination of a generator for continuously producing a currentof carrier frequency, frequency determining circuit, a transmissioncircuit to which oscillations are to be supplied by said generator,means for shunting said transmission circuit to control the applicationof oscillations thereto in accordance with signals, and means connectingsaid generator to said transmission circuit trans-- ant upon signalingfrom affecting the char- I actor of the oscillations produced bysaidgenerator.

12. The combination of a generator for continuously roducing a currentof carrier frequency, said generator including a tuned frequencydetermining circuit, a transmission circuit to which oscillations arewho supplied by said generator, means for shunting said transmissioncircuit to control the application of oscillations thereto in accordancewith Y signals, a one-way conductin circuit connecting said generatorto' sai transmission circuit transferring oscillations therebetweenwhich substantially prevents any change in the impedance of saidtransmission circuit attendant upon signaling from affecting thecharacter of the oscillations produced by said generator.

13. The combination of a generator for continuously producing a currentof carrier frequency, said generator including a tuned frequencydetermining circuit, a transmission circuit to which oscillations are tobe supplied by said generator, means for shunting said transmissioncircuit to'control the application of oscillations thereto in accordancewith signals, a circuit including a series resistance, connecting saidgenerator to said transmission circuit transferring oscillationstherebetween, said resistance having such magnitude as to substantiallyprevent any change in the impedance of said transmission circuitattendant upon signaling from afieco ing the character of theoscillations produced by said generator.

14. The combination of a generator for continuously producing a currentof carrier frequency, said generator including a tuned frequencydetermining circuit. a transmission circuit to which oscillations are tobe supplied by said generator, means for shunting said transmissioncircuit to control the application of oscillations thereto in accordancewith signals, and means connecting said generator to said transmissioncircuit transferring oscillations therebetween which substantiallyprevents any change in the impedance of said transmission circuit attendant upon signaling from changing the frequency of the oscillationsproduced by said generator.

15. A generator for continuously producing a current of carrierfrequency, an impedance to which said generator supplies current, a loadcircuit, means for shunting said load circuit in accordance with signalsand a circuit including a series resistance connecting said load circuitto' said impedance eleme t, said resistance having such magnitude as toefiectively prevent any tendency tashort-circuit said impedance e ement.g y

16. The combination of an oscillator, for continuously producingoscillations, which includes a tuned frequency determining circuit andan oscillating current output branch, a transmission circuit, means forconnecting said output branch to said transmission circuit, and a fixedresistance adapted to substantially prevent changes in the impedance ofthe circuit external to said output branch from afi'ecting the characterof the oscillations produced by said oscillator.

17. The combination of an oscillator, for continuously producingoscillations, which includes a tuned frequency determining circuit andan oscillating current output branch, a transmission circuit, and meansfor connecting said output branch to said transmission circuit includinga fixed resistance adapted to substantially prevent changes in theimpedance of the circuit external to said output branch from affectingthe character of the oscillations produced by said oscillator.

In witness whereof, I hereunto subscribe my name this 16th day ofDecember A. D.. 1920.

HARALD J. VENNES.

